Laser imaging systems are commonly used to produce photographic images from digital image data generated by magnetic resonance (MR), computed tomography (CT) or other types of scanners. Systems of this type typically include a continuous tone laser imager for exposing the image on photosensitive film, a film processor for developing the film, and an image management subsystem for coordinating the operation of the laser imager and the film processor.
The digital image data is a sequence of digital image values representative of the scanned image. Image processing electronics within the image management subsystem process the image data values to generate a sequence of digital laser drive values (i.e. exposure values), which are input to the laser scanner. The laser scanner is responsive to the digital laser drive values for scanning across the photosensitive film in a raster pattern for exposing the image on the film.
The continuous tone images used in the medical imaging field have very stringent image-quality requirements. A laser imager printing onto transparency film exposes an image in a raster format, the line spacing of which must be controlled to better than one micrometer. In addition the image must be uniformly exposed such that the observer cannot notice any artifacts. In the case of medical imaging, the observers are image analysts (e.g., radiologists).
In order to attain image quality of the required degree, it is important that all of the elements of the imager system handle the sheet of photosensitive film smoothly and efficiently without doing anything to degrade the images that ultimately appear on the film. The film is moved between the various stages of the exposure and development process using roller pairs that engage the sheet in their nip and drive it along a film transfer or transport path.
In conventional imaging apparatus, film transport rollers are mounted on bearing assemblies attached to frame side plates on both sides of the film transfer path that must be moved in order to install the rollers. The roller shafts extend through the side plates, which may be part of the imaging apparatus frame, making it very difficult to remove a roller or perform maintenance thereon, once they have been installed. Particularly where multiple film transport roller paths are used, it may be very difficult to manipulate the plates to install multiple rollers in premounted bearing sets. Further, in the imaging system it is also a continuing concern that static electricity build up on the film be managed because of the potential for the build up of static electricity to cause artifacts or a degraded image on the film, or cause the sheets of film to stick to the rollers.
It is desirable to have a film drive roller assembly for use in an imaging system that may be installed between two rigid plates as a preassembled assembly and does not require movement of the plates to install the rollers into their bearing sets. Further, it is also desirable to manage static electricity build-up on transported sheet material by providing static electricity dissipation characteristics for the rollers and bearings so that static electricity is dissipated to the frame of the imaging system from the surface of the film.